Persistent organic pollutants (POPs) refer to the highly toxic and hydrophobic organic compounds left and migrated in the environment and bio-accumulated in human and animal tissue. POPs in the environment mainly occur in the organic phase of sediment, having higher concentrations in pore water (water filling the spaces between grains of sediment). The hydrophobic organic compounds dissolved in natural water, including the water located in sediment pores, are cycled in ecosystems through evaporation, dissolution, adsorption and biological absorption processes. As the hydrophobic organic compounds have potential significant impacts on human health and the environment, it is important to accurately evaluate the density and biological effectiveness of the hydrophobic organic compounds dissolved in water, thus as a major carrier the sediment pore water sampling is necessary and important for water quality supervision against the persistent and hydrophobic organic pollutants.
Approaches for water sampling can be divided into two groups: passive and active approaches. As one of the most common active approaches, centrifugation may lead to the analysis results on the high side as its samples isolated by possibly excessive centrifugal speeds contain the pollutants dissolved in the inner water of the sediment particles. On the contrary, the passive approaches collect high-distribution-coefficient extraction medium rich samples; no additional power is required, thus applicable for uses in wild environment monitoring. The existing passive sediment pore water sampling mainly include two types of approaches: in-situ solid-phase micro-extraction and low-density polyethylene membrane extraction.
The in-situ solid phase micro-extraction instruments use high polymer coatings as adsorption medium, protecting the micro-extraction membranes as well as filtering out particles through using porous copper tubes and glass fiber membranes, however the adsorption membrane used herein are relatively expensive and easy to get damaged as well, because of this, it is inapplicable in field uses. The low density polyethylene membrane micro-extraction techniques use polyethylene membranes as adsorption medium, as in use the adsorption membranes are in direct contact with sediments, the particles adhered to the membranes may interference the determination results.
The abovementioned two types of water sampling approaches even have a drawback in common, which is difficult to collect water samples from different depths of a same position, and thus the water sampled cannot reflect the concentration changes over time.